Heating cable

This is the way I have set up my hot beds in the past, the 2in. layer at the base ensures that there is no overheating of the wooden floor and the same with the cover above the cable, and though the most important factor with a hot bed is keeping it moist, I have now removed the heating cable and replaced it with a shorter cable, but before fitting it I run both around the greenhouse (if the cable is warm it is easier to install as it is more flexible) and there was a definite difference in temperature between them, the new one we a lot cooler, so evidently it's a faulty cable, so if you ever buy a cable test it immediately to make sure its ok